Cranial neural crest cells migrate in highly specific pathways in the embryo and differentiate into many craniofacial structures. In an approach toward characterizing the factors which specify the migratory pathways, we are examining the interactions of these cells in vitro with the extracellular matrix molecules, collagen and fibronectin, which surround the migratory cells. We are also examining possible chemotactic respones of the neural crest cells to a variety of growth factors. Neural crest cells cultured in the presence of calf serum differentiate into melanocytes. We have isolated a factor from calf serum which promotes melanogenesis of neural crest cells and of a melanoma cell line.